This invention relates to a vertical axis wind turbine constructed in such a way that the wind energy captured can be considerably increased for a given rotor size in comparison with conventional vertical axis wind turbines.
It should not be forgotten that VAWT (Vertical Axis wind Turbines) have a number of characteristics that clearly distinguish them from HAWT (Horizontal Axis Wind Turbines), such as    they do not require great height above the ground, as a result of which they can be easily concealed in the environment and thus avoid the visual effect produced by the latter,    maintenance and damage repair are very much easier than in the case of HAWT as both the generator and the rotor are very close to the ground,    the impact on birds is virtually non-existent,    the dynamics of the blades are very much simpler and the structure is more reduced, and therefore more economical,    the rotation speed is very much slower than in the case of HAWT, which has an effect on both wear in the mechanisms and the noise produced during rotation. Also this noise can be eliminated by making the rotors supported by MagLev (Magnetic Levitation) force,    with a correct configuration of the rotors and the mechanisms transmitting movement to the generator it is possible to eliminate the multiplying mechanisms present in HAWT, which are heavy mechanical components very prone to suffering damages,    VAWT wind turbines nave a very much lower rotation start speed end a higher safety cut-off speed than HAWT, which means that they can make much greater use of existing winds. Furthermore the configuration illustrated in this document has the ability to fold up all the blades and remain closed (without any blade taking the wind), thus avoiding possible damage when winds are excessively high, without this resulting in damage to the structure of the wind turbine or the supporting structure.
Two reference models have been proposed so far in the concept of vertical axis wind turbines:
The “SAVONIUS” model, developed by the Finnish engineer Sigurd J. Savonius in 1992. Through the special arrangement of its blades this model gives rise to the problem that in the return direction the inactive blades offer great resistance to the wind and this counteracts the effect of the wind on the active blades.
The second model, the “DARRIEUS” model, developed by the French engineer Georges Darrieus, provided a solution to the problem with the “SAVONIUS” model but the excessively small surface area responsible for gathering the force of the wind makes it rather inefficient.
Documents EP 1096144 and FR 2913254 disclose vertical axis wind turbines comprising first and second independent coaxial rotors with the ability to rotate in different directions. Each of the rotors comprises vertically arranged fixed blades. The second rotor is located above the first. The blades of each rotor thus travel in different areas.
Documents ES 1065927U and ES 280117U disclose vertical axis wind turbines comprising first and second independent coaxial rotors with the ability to rotate in different directions. Each of the rotors comprises blades which can be folded on a horizontal axis. The blades of each rotor travel in different areas, and one of the areas is above the other.
In general the vertical axis wind turbines developed so far have been less efficient than horizontal axis turbines.
The purpose of this invention is to overcome the problems stated through a vertical axis wind turbine constructed in such a way that a considerable increase in its efficiency can be achieved, making it comparable with horizontal axis turbines.
The vertical axis wind turbine according to the invention comprises a structure which allows two rotors to rotate simultaneously in the same horizontal plane, in a clockwise direction and an anticlockwise direction. This fact makes it possible to double, in the same space, the energy which the wind produces as it passes through the rotor. In order to achieve this effect the wind turbine blades are deployed or folded depending upon the rotational position in which they are to be found in such a way that while in one direction the rotor blades rotating clockwise are deployed, taking advantage of all the thrust provided by the inertia of the wind, the blades of the other rotor are folded, so that in the first case they do not offer any resistance to the wind and in the second case they do not interfere with the blades of the other rotor rotating in the opposite direction.
The vertical axis wind turbine according to the invention comprises first and second independent coaxial rotors, both having a vertical axis. These two rotors are mounted on the same vertical shaft with the ability to rotate in different directions. The first and second rotors mentioned bear blades which are articulated to the said rotors on non-coinciding vertical axes. These blades have a curved active surface in the same direction for all the blades on each rotor, but in a direction opposite to that of the blades on the other rotor.
This structure allows the two rotors to rotate simultaneously, one of the rotors rotating clockwise and the other anticlockwise. In this way the area swept by the blades on the first rotor can at least partly coincide with the area swept by the blades of the second rotor.
In order to achieve this the blades of the first rotor are preferably articulated to the first rotor through articulated connections located at a greater height than that at which the connections through which the blades of the second rotor are articulated to the second rotor are located.
Through a mechanism, for example based on pinions, the force of the two rotors can be applied to the same output shaft, which will constitute the output shaft of the wind turbine.
Preferably the blades of the two rotors are related to their axes of rotation through opposite edges on one rotor and the other.
Thanks to the articulation of the blades, the blades of the two rotors whose convex surfaces are directed opposite the direction of the wind at any time will be folded in, thus substracting no energy to the rotor. On the contrary those blades whose concave surfaces are directed against the force of the wind will be deployed to receive the full force of the wind.
Folding and unfolding of the blades takes place progressively according to the rotation of the corresponding rotors, and the blades will change from positions having a maximum active orientation to positions having a minimum active orientation.
According to a preferred embodiment the blades of the first rotor are articulated to the rotor through the upper extremity of the axis for articulation of these blades, while the blades of the second rotor are articulated to the second rotor through the lower extremity of the axis articulating the blades of this second rotor.
In an even more preferred embodiment the articulation connections through which the blades of the first and second rotors are articulated are located mid-way up the blades.
These arrangements prevent the blades on one of the rotors from striking those of the other during the operations of folding and unfolding when the rotors rotate in opposite directions.
In one embodiment of the wind turbine according to the invention the first rotor includes an upper annular support to which the articulation axis of the blades of this first rotor is related, for example having the articulation connection for the blades of the first rotor located upon it. For its part the second rotor comprises a lower annular support to which the articulation axis of the blades of the second rotor is related, the articulation connection for the blades of the second rotor being located upon it.
The two annular supports are parallel and coaxial. As already indicated the connection between the blades and the corresponding annular support may be made for example through the mid-point of the articulation axis, through the upper extremity of that axis in the case of the upper support and the lower extremity in the case of the lower support.
The blades have a concave surface on one side and a convex surface on the opposite side. The blades may for example be cylindrical surfaces having vertical axes, all with the same curvature, being related through one of their straight vertical edges to the articulation axis of the corresponding rotor, this edge being the opposite one for the blades of one rotor and the other.
The blades of the two rotors may be located in coincident angular positions on the two rotors.
The arrangement described permits to arrange a vertical axis wind turbine which includes a simple sensor mechanism whereby the blades are folded in when they are on the return path, offering zero resistance to the wind, but deploy when the blades face the effect of the wind, offering total resistance. The mentioned sensor mechanism may comprise merely the articulation of the blades to the rotor in the form already described. Taking advantage of the fact that the blades are folded in for approximately 50% of their path and are folded out for the other approximately 50% it is possible for the two rotors whose blades are folded in and deployed at opposite times or positions to be included in the same mechanism, thus increasing the effectiveness of the wind turbine over approximately 100% of the path of the blades or rotation of the wind turbine. Likewise, the blades may be operated by another type of sensor mechanism, servo motors, guides, etc.
For a better understanding, drawings of embodiments of the wind turbine according to this invention are appended by way of an explanatory but not restrictive example.